Summary

The human health effects of Btk are only one aspect of its effect on
the
environment. This page attempts to survey current literature, mostly
peer
reviewed, to present a balanced picture of problems that could
eventually
arise when Bt is introduced on a large scale into a populated setting.
There are no long-term studies of health effects to date, so the
information
presented here allows you to make up your own mind as to whether it is
a good idea to spray Bt on humans or not.

We summarize the points made in the literature and remarks
below:

Bt is the same cellular organism as B. cereus (causes
gastroenteritis)
and B. anthracis (causes anthrax). The only difference is in one
"organelle"
of the cell, called a plasmid, that produces proteins. Each plasmid
produces
a unique protein that attacks a target life form. In the case of Bt,
that
life form is a caterpillar or other insect life forms.

Can Bt become anthrax? Theoretically, yes - it could
exchange a
plasmid
with a wild anthrax germ. Also, it is not easy to tell anthrax, B.
cereus,
and Bt apart - they look the same and grow in the same environments,
and
even test the same in some genetic tests. See this
Seattle Weekly article for an interesting view.

When Bt is sprayed, it can and does infect many people in
the
target
zone,
setting up colonies in their respiratory tract and maybe in their
intestines
that live for weeks or months. The effects of this are not known.
Obvious
symptoms do not appear, but what could happen years from now as a
result
of these infections is anyone's guess. It is suspected that
"symptomless"
infections can challenge the immune system and cause disease later
(diabetes,
multiple sclerosis, and lupus are some under consideration).

There is growing evidence that exposure to inhaled
bacterial
antigens that generate immune responses in humans (a potential for
allergic reactions) can trigger skin allergic reactons of various types
in some individuals. Bt falls into this category. Epidemiological
studies have so far almost completely ignored dermatological symptoms.
There are a significant number of anecdotal reports of skin symptoms
after sprayings of Bt products in New Zealand (see New
Zealand CC-PAM Health Incident Report at this link).

The same Bt pesticides that are sprayed on crops produce
detectable residues in foods, even processed foods such as pasta.
Gastroenteritis (food poisoning or "stomach flu") can result. It is
estimated that a sizeable percentage of such diseases that were
previously thought to be caused by B. cereus are actually
caused by Bt insecticides.

People with sensitive immune systems could be affected in
ways we
do not
yet know, but immune responses are seen when Bt infections establish in
humans.

Closing your house up will not prevent Bt from getting in.
Staying
indoors
for even one day after a spraying will still expose you to significant
amounts of Bt spores.

Bt endotoxins may cause unexpected effects; for instance,
some
insects
consuming genetically modified crops that produce Bt endotoxin actually
grow faster. This could because the toxin is actually being used as
food,
but in experiments the insects had all the preferred food they could
eat.
An even more probable reason could be that Bt endotoxin acts as a
hormone
mimicing substance (this is not the first bacterial toxin to show this
behavior). These types of substances (also called endocrine disrupters)
are increasingly suspected of causing serious health problems in humans.

Bt endotoxins are not completely
destroyed in the acidic environment in the human gut, as previously
claimed. These toxins are detectable in blood after exposure, and they
cross the placental barrier. This presents serious issues especially
for pregnant women in spray zones. See (12) below.

Can Bt live in Humans?

This is an interesting question. There are no absolutely definitive
studies
addressing this issue, but there is a good deal of circumstantial
evidence
that Bt can and does survive and grow in humans:

The culture media used to grow Bt in the lab is the same
media
used to
grow other human pathogenic bacteria.

The conditions for growth of Bt (pH 7.4, temperature 37oC,
moist
environment)
are found in humans.

Humans develop antibodies to the Bt organism.

Even four months after a single exposure, Bt organisms of
the
same
strain
as the pesticide used in the exposure can be cultured from nasal swabs.
It is unlikely that the original spores would still be present after
this
period of time.

There are a few studies that show Bt canand does cause
gastroenteritis
in humans and that you can recover culturable Bt from nursery workers
feces,
indicating that Bt can live and grow in the intestinal tract.

When humans are infected in this way, the immune system of healthy
individuals
probably fights off and eventually destroys the invading cells.
However,
there are some indications that Bt is able to survive for quite some
time
at a level that does not cause any overt signs of disease.

Survey Papers

No Spray Zone has prepared survey paper, available
here, that reviews the current literature (through 2005) on Bt and
its human health effects. The paper assumes some knowledge of medical
and biological terminology. In addition, a 2006 article published in
the Journal of Pesticide Reform
presents the information in the NSZ survey paper in a less technical
form. You can find it here.
Both
of these articles have good bibliographies that are more
exhaustive than the list below.

Sources
(In most cases, if a paper is cited, the abstract of the paper is
given.)

(1)This study shows that Bt can and does infect humans via
inhalation.
The infections are asymptomatic in healthy individuals and last at
least
for a few months. The immune responses noted are a little disturbing
because
not only will some people develop allergies to Bt, but there is some
evidence
that chronic diseases such as Gulf War syndrome, fibromyalgia, MCS,
rheumatoid
arthritis, and other autoimmune diseases may be partly caused by these
"subclinical" infections by organisms heretofore considered to be
harmless.

Although health risks to pesticides containing Bacillus
thuringiensis
(Bt) have been minimal, the potential allergenicity of these organisms
has not been evaluated. Therefore, a health survey was conducted in
farm
workers before and after exposure to Bt pesticides. Farm workers who
picked
vegetables that required Bt pesticide spraying were evaluated before
the
initial spraying operation (n = 48) and 1 and 4 months after (n = 32
and
20, respectively). Two groups of low- (n = 44) and medium- (n = 34)
exposure
workers not directly exposed to Bt spraying were also assessed. The
investigation
included questionnaires, nasal/mouth lavages, ventilatory function
assessment,
and skin tests to indigenous aeroallergens and to a variety of Bt spore
and vegetative preparations. To authenticate exposure to the organism
present
in the commercial preparation, isolates from lavage specimens were
tested
for Bt genes by DNA-DNA hybridization. Humoral immunoglobulin G (IgG)
and
immunoglobulin E (IgE) antibody responses to spore and vegetative Bt
extracts
were assayed. There was no evidence of occupationally related
respiratory
symptoms. Positive skin-prick tests to several spore extracts were seen
chiefly in exposed workers. In particular, there was a significant (p
<
0.05) increase in the number of positive skin tests to spore extracts 1
and 4 months after exposure to Bt spray. The number of positive skin
test
responses was also significantly higher in high (p < 0.05) than in
low-
or medium-exposure workers. The majority of nasal lavage cultures from
exposed workers was positive for the commercial Bt organism, as
demonstrated
by specific molecular genetic probes. Specific IgE antibodies were
present
in more high-exposure workers (p < 0.05) than in the low and medium
groups. Specific IgG antibodies occurred more in the high (p < 0.05)
than in the low-exposure group. Specific IgG and IgE antibodies to
vegetative
organisms were present in all groups of workers. Exposure to Bt sprays
may lead to allergic skin sensitization and induction of IgE and IgG
antibodies,
or both.

(2)This recent study shows that anthrax and Bt are virtually
the
same organism. In fact, it is clear that Bt could become anthrax,
if
the right plasmids were available.

Remarkably, it appears that the ubiquitous soil-living
bacterium and
occasional food-poisoning culprit Bacillus cereus, the widely used
insect
biocontrol pathogen Bacillus thuringiensis, and the life-threatening
biological
warfare agent Bacillus anthracis are the same species, despite the
striking
differences in phenotype. The secret appears to lie in the plasmids
harboured
by B. anthracis and B. thuringiensis. When ten B. cereus-like strains
were
isolated for biochemical and genetic analysis from soil taken from
anthrax
outbreak sites, they were found by Helgason et al. to have the same
chromosomal
marker as the implicated B. anthracis strains, but no plasmids. In
their
natural environments these species have a relatively low rate of clone
formation, and it is known that all three Bacillus species are
naturally
able to take up plasmids. Indeed, plasmid exchange between B. cereus
and
B. anthracis has been verified experimentally. However, before sounding
a general alarm, it cannot be ruled out that there is some other
special,
but as yet undetected, feature of the B. anthracis genome that makes it
alone of the three species particularly adept at retrieving and
retaining
virulence plasmids.

(3)
This paper states that the difference between Bt and B. cereus is
virtually nil. B. cereus causes acute gastroenteritis and meningitis.

A complete physical map of a Bacillus thuringiensis
chromosome

Carlson-CR; Kolsto-AB J-Bacteriol. 1993 Feb; 175(4): 1053-60

Bacillus thuringiensis is the source of the most widely used
biological
pesticide, through its production of insecticidal toxins. The toxin
genes
are often localized on plasmids. We have constructed a physical map of
a Bacillus thuringiensis chromosome by aligning 16 fragments obtained
by
digestion with the restriction enzyme NotI. The fragments ranged from
15
to 1,350 kb. The size of the chromosome was 5.4 Mb. The NotI DNA
fingerprint
patterns of 12 different B. thuringiensis strains showed marked
variation.
The cryIA-type toxin gene was present on the chromosome in four
strains,
was extrachromosomal in four strains, and was both chromosomal and
extrachromosomal
in two strains. A Tn4430 transposon probe hybridized to 5 of the 10
cryIA-positive
chromosomal fragments, while cryIA and the transposon often hybridized
to different extrachromosomal bands. Ten of the strains were hemolytic
when grown on agar plates containing human erythrocytes. Nine of the
strains
were positive when assayed for the presence of Bacillus cereus
enterotoxin.
We conclude that B. thuringiensis is very closely related to B. cereus
and that the distinction between B. cereus and B. thuringiensis should
be reconsidered.

(4)Here is an example how acute toxic shock effects and longer
lasting
infections can result from Bt exposure. Of course, 100,000,000 spores
in
your nose is a lot of product. However, it does establish that
infection
can occur, and you can postulate in cases of weak immune response that
an infection with a lower initial dose could be troublesome.

Bacillus thuringiensis serotype H34 isolated from human and
insecticidal
strains serotypes 3a3b and H14 can lead to death of immunocompetent
mice
after pulmonary infection

Hernandez,E; Ramisse,F; Cruel,T; le Vagueresse,R; Cavallo,JD

FEMS-Immunol-Med-Microbiol. 1999 May; 24(1): 43-7

In 1995, we isolated a strain of Bacillus thuringiensis
serotype H34
from severe human tissue necrosis. This bacterium was able to induce
myonecrosis
in immunosuppressed mice after cutaneous infection. Its potential
pathogenicity
for immunocompetent hosts was investigated in a mouse model of
pulmonary
infection. Mice infected intranasally by a suspension containing 10(8)
spores died within 8 h in a clinical toxic-shock syndrome. In the same
conditions, infection with a mutant without crystalline toxin, with the
supernatant from a culture containing 108bacteria/ml and by
the insecticidal strain serotypes 3a3b or H14 led to identical results.
Lower inocula simply induced a local inflammatory reaction with
bacterial
persistence observed during the course of 10 days.

(5)The study published by Green et al, is touted by agriculture
departments
and others as proof of no health effects. In fact the only conclusion
was
that the level of risk for Btk and other existing or future microbial
pesticides
in immunocompromised hosts deserves further study. This study was not,
as we have been trying to point out, looking for long-term effects. To
date there has never been one on Btk.

Bacillus thuringiensis var. kurstaki (B.t.-k) is a microbial
pesticide
which has been widely used for over 30 years. Its safety for a human
population
living in sprayed areas has never been tested. Surveillance for human
infections
caused by B.t.-k among Lane County, Oregon residents was conducted
during
two seasons of aerial B.t.-k spraying for gypsy moth control. Bacillus
isolates from cultures obtained for routine clinical purposes were
tested
for presence of Bacillus thuringiensis (B.t.). Detailed clinical
information
was obtained for all B.t.-positive patients. About 80,000 people lived
in the first year's spray area, and 40,000 in the second year's area. A
total of 55 B.t.-positive cultures were identified. The cultures had
been
taken from 18 different body sites or fluids. Fifty-two (95 percent) of
the B.t. isolates were assessed to be probable contaminants and not the
cause of clinical illness. For three patients, B.t. could neither be
ruled
in nor out as a pathogen. Each of these three B.t.-positive patients
had
preexisting medical problems. The level of risk for B.t.-k and other
existing
or future microbial pesticides in immunocompromised hosts deserves
further
study.

(6)Apparently our own cells are not sufficiently different from
those
of insects so that we suffer no harm from Bt pesticide exposure. Two
Canadian
scientists have done a simple, elegant experiment and reported their
important
and disturbing findings at the American Society for Microbiology
conference
in Chicago, spring of 1999. In this study commercial Bt products
containing
Bacillus thuringiensis kurstaki spores and their parasporal inclusion
bodies
(Btk toxin) were tested for toxic effects on insect and human cells.

Presented at General Meeting, American Society of
Microbiologists,
May 1999, Chicago.

Quoting the study, "The patterns of damage to insect and human
cells
were the same". Their conclusion, "This study establishes for the first
time the cytotoxic effects of commercial Bt products, which are largely
target cell independent, resulting from an infection-like process."

(7)This study shows that even remaining indoors during an aerial
spray
does not save you from being exposed to Btk organisms. In fact, your
long-term
exposure may be greater in your home or office than if you camped
outside
for a few days after the spraying. Also, wind speed and direction are
major
factors in bacterial dispersal.

Spatial and Temporal Distribution of Airborne Bacillus
thuringiensis
var. kurstaki during an Aerial Spray Program for Gypsy Moth Eradication

We measured airborne exposures to the biological insecticide
Bacillus
thuringiensis var. kurstaki (Btk) during an aerial spray program to
eradicate
gypsy moths on the west coast of Canada. We aimed to determine whether
staying indoors during spraying reduced exposures, to determine the
rate
of temporal decay of airborne concentrations, and to determine whether
drift occurred outside the spray zone. During spraying, the average
culturable
airborne Btk concentration measured outdoors within the spray zone was
739 colony-forming units (CFU)/m3 of air. Outdoor air concentrations
decreased
over time, quickly in an initial phase with a half time of 3.3 hr, and
then more slowly over the following 9 days, with an overall half-time
of
about 2.4 days. Inside residences during spraying, average
concentrations
were initially 2-5 times lower than outdoors, but at 5-6 hr after
spraying
began, indoor concentrations exceeded those outdoors, with an average
of
244 CFU/m3 vs. 77 CFU/m3 outdoors, suggesting that the initial benefits
of remaining indoors during spraying may not persist as outside air
moves
indoors with normal daily activities. There was drift of culturable Btk
throughout a 125- to 1,000-meter band outside the spray zone where
measurements
were made, a consequence of the fine aerosol sizes that remained
airborne
(count median diameters of 4.3 to 7.2 µm). Btk concentrations
outside
the spray zone were related to wind speed and direction, but not to
distance
from the spray zone.

(8)Here is a quote from the USDA's Final EIS on Gypsy Moth
Control,
Appendix F Vol. III of V (Nov. '95) showing that there could be at
least
some difference in infectivity depending on the composition of the
bacterial
suspension:

"...several studies indicate that B.t.k. can be recovered from
exposed
mammals but that recovery decreases relatively fast after exposure is
terminated.
In this respect, the study by Oshodi and Macnaughtan (1990, Btk
preparation
manual by the manufacturer of Foray48B Novo Nordisk) is somewhat
unusual.
After inhalation exposure to Foray 48B, the numbers of viable B.t.k.
spores
recovered from the lungs [of mammals] did not decrease substantially
during
a 28-day observation period." (p. 4-6).

(9)It looks like Bt can actually
survive
in the gut of a human and set up residence there also.

Isolation and characterization of Bacillus cereus-like
bacteria
from
faecal samples from greenhouse workers who are using Bacillus
thuringiensis-based
insecticides

Abstract: Since the discovery of the insecticidal
activity
of
Bacillus thuringiensis at the beginning of the twentieth century, this
bacterium has been used increasingly against various insect pests. In
spite
of the extensive use of B. thuringiensis, only sporadic clinical
case reports have been published. In recent years, the close
relationship
between B. thuringiensis and the human pathogen Bacillus cereus has
been
confirmed. In practice, only the insecticidal activity of B.
thuringiensis
distinguishes the two species. However, both species are composed of
thousands
of isolates with varying potential for causing adverse effects in
humans.
The aim of this study was to employ molecular biology methods for
assessment
of occupational exposure to B. thuringiensis-based biopesticides by
determination
of specific genetic information including plasmid profiles and random
amplified
polymorphic DNA (RAPD). Methods: Faecal samples from 12 persons,
working
in Danish greenhouses, were collected for microbial analysis. Seven
persons
were using B. thuringiensis-based insecticides, whereas five persons
were
employed at greenhouses that did not use B. thuringiensis. The bacteria
were isolated on B. cereus-specific solid substrate, and colonies were
further identified using the polymerase chain reaction (PCR). The PCR
method
was used for the identification of the enterotoxin genes HblA and BceT.
The expression of enterotoxins was detected with two commercial
serological
kits. Primers specific for 16S-23S spacer region were used to identify
the bacteria as members of the B. cereus group. Several primers towards
insecticidal genes have been used in order to further characterize the
isolates as subspecies of B. thuringiensis.
Results: Two faecal samples from the B.
thuringiensis-exposed
greenhouse workers were positive for B. cereus-like bacteria. One
isolate
displayed intracellular crystalline inclusions characteristic of B.
thuringiensis,
production of and genes for B. cereus enterotoxins and it was
PCR-positive
for an insecticidal toxin primer set. RAPD profiles of the faecal
isolate
were identical to that of strains isolated from a commercial product.
Conclusions: The methods applied have verified that the faecal
isolate
was identical to the B. thuringiensis isolate found in the
biopesticide
used. This is the first reported case of isolation of a bacterial
biopesticide
from human faeces [emphasis NSZ].The biopesticide was shown to
harbour
and express enterotoxin genes. However, there is no evidence that this
caused any adverse effects to the person from whom these bacteria were
isolated.

Abstract
We present an idea that larvae of some Bacillus thuringiensis (Bt )
resistant populations of the diamondback moth, Plutella xylostella
(L.),
may be able to use Cry1Ac toxin derived from Bt as a supplementary food
protein. Bt transgenic crops could therefore have unanticipated
nutritionally
favourable effects, increasing the fitness of resistant populations.
This
idea is discussed in the context of the evolution of resistance to Bt
transgenic
crops.

Young farmers with cellular
reactivity to airborne microbes suffer more frequently from
work-related skin symptoms and
allergic dermatitis

R. Spiewak, C. Skorska, A. Góra1, A. Horoch, J.
Dutkiewicz

Ann Agric Environ Med 2001, 8, 255–259.

Abstract: 75 farming
students (49 males and 26 females aged 16–23 years) underwent
dermatological, laryngological and pulmonary examination, skin prick
tests with common and farm allergens, Phadiatop and total IgE
measurement. After that, the migration inhibition tests with antigens
of airborne microbes typical for farm environment (Saccharopolyspora rectivirgula, Pantoea
agglomerans, and Aspergillus fumigatus) were carried out.
Possible differences between students with positive results and those
non-reactive were sought.
Results: 10 students reacted to at least one microbial antigen in the
migration inhibition test. There were no significant differences in
distribution of atopy, prick test results, total IgE, and Phadiatop
between the reactive students and their classmates. Only one case of
asthma was found, hence a further statistical analysis was not
feasible. Allergic rhinitis has been found in 30% of the reactive and
in 9.2% of non-reactive students; the difference, however, was not
statistically significant (p = 0.06). Significant differences were
found with respect to the frequency of allergic skin diseases (40%
reactive versus 9.2% non-reactive, p = 0.009); no other triggering
factors than microbial antigens could be identified in 2 out of 4
reactive students with dermatitis. Work-related symptoms were present
in all reactive students (100% versus 27.7%, p = 0.001); 8 out of 10
reactive students did not show any other specific sensitisation.
Antigens of airborne microbes are commonly associated with lung
diseases. Our results, however, suggest that the skin may be affected
as well. Relatively strong association between cellular reactivity to
airborne microbes and skin diseases deserves further studies.

Pesticides associated to genetically modified foods (PAGMF),
are
engineered to tolerate herbicides such as glyphosate (GLYP) and
gluphosinate (GLUF) or insecticides such as the bacterial toxin
bacillus thuringiensis (Bt). The aim of this study was to evaluate the
correlation between maternal and fetal exposure, and to determine
exposure levels of GLYP and its metabolite amino methylphosphoricacid
(AMPA), GLUF and its metabolite 3-methylphosphinicopropionicacid
(3-MPPA) and Cry1Abprotein (a Bt toxin) in Eastern Townships of Quebec,
Canada. Blood of thirty pregnant women (PW) and thirty-nine non
pregnant women (NPW) were studied. Serum GLYP and GLUF were detected in
NPW and not detected in PW. Serum 3-MPPA and CryAb1 toxin were detected
in PW, their fetuses and NPW. This is the first study to reveal the
presence of circulating PAGMF in women with and without pregnancy,
paving the way for a new field in reproductive toxicology including
nutrition and utero-placental toxicities.

Conclusions

To our knowledge, this is the first study to highlight the
presence of pesticides-associated genetically modified foods in
maternal, fetal and non pregnant women’s blood. 3-MPPA and Cry1Ab toxin
are clearly detectable and appear to cross the placenta to the fetus.
Given the potential toxicity of these environmental pollutants and the
fragility of the fetus, more studies are needed, particularly those
using the placental transfer approach.

Thus, our present results will provide baseline data for
future
studies exploring a new area of research relating to nutrition,
toxicology and reproduction in women. Today, obstetric-gynecological
disorders that are associated with environmental chemicals are not
known.